Trading kidneys, repugnant markets and stable marriages win the Nobel Prize in Economics

Roth and Shapley charted a course for economists to go beyond simply arguing for markets in everything.

The 2012 Nobel Prize in Economics - technically the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, but nobody cares - has been awarded to two American Economists, Alvin Roth and Lloyd Shapley "for the theory of stable allocations and the practice of market design". The Nobel Committee explains what that means:

This year's Prize concerns a central economic problem: how to match different agents as well as possible. For example, students have to be matched with schools, and donors of human organs with patients in need of a transplant. How can such matching be accomplished as efficiently as possible? What methods are beneficial to what groups? The prize rewards two scholars who have answered these questions on a journey from abstract theory on stable allocations to practical design of market institutions.

Lloyd Shapley used so-called cooperative game theory to study and compare different matching methods. A key issue is to ensure that a matching is stable in the sense that two agents cannot be found who would prefer each other over their current counterparts. Shapley and his colleagues derived specific methods – in particular, the so-called Gale-Shapley algorithm – that always ensure a stable matching. These methods also limit agents' motives for manipulating the matching process. Shapley was able to show how the specific design of a method may systematically benefit one or the other side of the market.

Alvin Roth recognized that Shapley's theoretical results could clarify the functioning of important markets in practice. In a series of empirical studies, Roth and his colleagues demonstrated that stability is the key to understanding the success of particular market institutions. Roth was later able to substantiate this conclusion in systematic laboratory experiments. He also helped redesign existing institutions for matching new doctors with hospitals, students with schools, and organ donors with patients. These reforms are all based on the Gale-Shapley algorithm, along with modifications that take into account specific circumstances and ethical restrictions, such as the preclusion of side payments.

Even though these two researchers worked independently of one another, the combination of Shapley's basic theory and Roth's empirical investigations, experiments and practical design has generated a flourishing field of research and improved the performance of many markets. This year's prize is awarded for an outstanding example of economic engineering.

The committee have yet again reaffirmed the old adage that the most important thing to do when trying for a nobel prize is to live long enough that your achievements are recognised. The Gale-Shapley algorithm, for instance, was devised in 1962, when Lloyd Shapley was 34. It concerns a maths problem known as the stable marriage problem: if you have an even number of men and women, can you always come up with a set of marriages where there are no two people of opposite sex who would both rather have each other than their current partners? (1960s maths problems: usually heteronormative.) If you can, then the marriage is "stable".

The Gale-Shapley algorithm is a way of always ensuring stable matches; and much of Shapley's work covers the same areas, straddling the boundaries between economics, mathematics, and computer science.

Roth is the younger of the two winners, and works in a far more empirical sphere. As the committee points out, although the two men never actually collaberated, Roth took Shapley's theoretical work and applied it to actually existing markets. For instance, Roth used the Gale-Shapley agorithm to ease the kidney shortage in the US. David Wessel explains (£):

As of noon yesterday, 58,470 people in the U.S. were waiting for a kidney transplant. Most won't get one this year. There aren't enough donated kidneys to go around. Surgeons transplanted just 15,129 kidneys last year. Now a band of transplant surgeons and economists are trying to fix that by creating a moneyless market for exchanging kidneys. Most transplanted kidneys come from a person who has died, a supply that grows slowly because of ignorance about the need for donations or grieving relatives' reluctance. But a kidney taken from a live donor works better, and almost everyone has a spare. As techniques improve for removing healthy kidneys and for suppressing the body's tendency to reject a transplant, doctors increasingly turn to kidneys from living donors, usually relatives. Last year, 43% of kidneys transplanted in the U.S. came from living donors, up from 28% a decade ago. But a biological barrier often blocks a transplant from a relative. In about a third of all would-be pairs, blood types are incompatible. In others, the sick person has antibodies that can initiate a rejection of the donated organ. It's heartbreaking "to have the treasure of the live donor and then have that not go forward because of a biological obstacle," says Massachusetts General Hospital transplant surgeon Francis DelMonico.

Occasionally, transplant centers spot a way out: One New England father with blood type A couldn't donate a kidney to his daughter with blood type B. So he gave a kidney to a teenager with blood type A, and the teenager's sister gave a kidney for the man's daughter. New England's transplant centers have done six such exchanges. Baltimore's Johns Hopkins University has done seven.

The crucial thing about Roth's work, from an economic point of view, is that it involves finding stable allocations using market-like situations without involving money. The kidney swaps in the New England situation are market-like, trading kidneys for kidneys in a way that makes all parties better-off, but they don't actually require kidneys to be bought and sold.

We can see the importance of this by looking at another paper of Roth's, not cited by the committee, on repugnance in markets (pdf). Roth demonstrates that some markets are limited because the very existance of a market in some goods is considered repugnant. He argues, for instance, that the trade in horse meat being banned in California is not done through fears that eating horse meat is unsafe; nor is it done for animal welfare reasons, since it is still legal to farm and kill horses. But banned it is, and Roth argues that the natural response of economists to situations of this type - to argue for freer markets - is wrong, since it ignores the very strong feelings involved in the situation. Instead:

Being aware of the sources of repugnance can only help make such discussions more productive, not least because it can help separate the issues that are fundamentally empirical—like the degree of crowding out of altruistic donations that might result from different incentive schemes compared to how much new supply might be produced—from areas of disagreement that are not primarily empirical.

Hopefully his new Nobel Prize should give that argument greater weight in the years ahead.

A patient receives a kidney in Johns Hopkins university in Baltimore. Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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I was wrong about Help to Buy - but I'm still glad it's gone

As a mortgage journalist in 2013, I was deeply sceptical of the guarantee scheme. 

If you just read the headlines about Help to Buy, you could be under the impression that Theresa May has just axed an important scheme for first-time buyers. If you're on the left, you might conclude that she is on a mission to make life worse for ordinary working people. If you just enjoy blue-on-blue action, it's a swipe at the Chancellor she sacked, George Osborne.

Except it's none of those things. Help to Buy mortgage guarantee scheme is a policy that actually worked pretty well - despite the concerns of financial journalists including me - and has served its purpose.

When Osborne first announced Help to Buy in 2013, it was controversial. Mortgage journalists, such as I was at the time, were still mopping up news from the financial crisis. We were still writing up reports about the toxic loan books that had brought the banks crashing down. The idea of the Government promising to bail out mortgage borrowers seemed the height of recklessness.

But the Government always intended Help to Buy mortgage guarantee to act as a stimulus, not a long-term solution. From the beginning, it had an end date - 31 December 2016. The idea was to encourage big banks to start lending again.

So far, the record of Help to Buy has been pretty good. A first-time buyer in 2013 with a 5 per cent deposit had 56 mortgage products to choose from - not much when you consider some of those products would have been ridiculously expensive or would come with many strings attached. By 2016, according to Moneyfacts, first-time buyers had 271 products to choose from, nearly a five-fold increase

Over the same period, financial regulators have introduced much tougher mortgage affordability rules. First-time buyers can be expected to be interrogated about their income, their little luxuries and how they would cope if interest rates rose (contrary to our expectations in 2013, the Bank of England base rate has actually fallen). 

A criticism that still rings true, however, is that the mortgage guarantee scheme only helps boost demand for properties, while doing nothing about the lack of housing supply. Unlike its sister scheme, the Help to Buy equity loan scheme, there is no incentive for property companies to build more homes. According to FullFact, there were just 112,000 homes being built in England and Wales in 2010. By 2015, that had increased, but only to a mere 149,000.

This lack of supply helps to prop up house prices - one of the factors making it so difficult to get on the housing ladder in the first place. In July, the average house price in England was £233,000. This means a first-time buyer with a 5 per cent deposit of £11,650 would still need to be earning nearly £50,000 to meet most mortgage affordability criteria. In other words, the Help to Buy mortgage guarantee is targeted squarely at the middle class.

The Government plans to maintain the Help to Buy equity loan scheme, which is restricted to new builds, and the Help to Buy ISA, which rewards savers at a time of low interest rates. As for Help to Buy mortgage guarantee, the scheme may be dead, but so long as high street banks are offering 95 per cent mortgages, its effects are still with us.